PROJECTSUMMARY/ABSTRACT Manyleadingcausesofdeathhavedeclinedsignificantlyoverthepast100years(e.g.,tuberculosis, pneumonia/influenza,gastritis);?however,thesuiciderateisvirtuallyidenticaltowhatitwas100years ago. Lack of progress in the prevention of suicide is due in large part to the limited understanding of thisproblem.Suicidalthoughtsandbehaviors(STBs),likeotherbehaviorproblems(e.g.,alcoholuse, substanceuse,eatingdisorders),rarelyoccurintheresearchlabwheretheycanbecarefullyprobed and cannot be ethically induced in the lab. As a result, experts lack a firm understanding of the fundamental properties of STBs, and of how, why, and when they unfold in nature. The purpose of this study is to address this enormous gap by using newly developed smartphone and wearable biosensortechnologiestoconductanintensivelongitudinalstudythatwilladvancetheunderstanding andpredictionofSTBsandrelatedbehaviors.Thisstudywillmonitor600people(300adultsand300 adolescents) at elevated risk of STBs (i.e., those presenting to a psychiatric hospital with suicide ideationand/orarecentsuicideattempt)duringahighrisktimeperiod(i.e.,post-hospitalization).The first aim of this study is to identify digital phenotypes of STBs using data collected both actively/subjectively using repeated smartphone surveys and passively/objectively using continuous data from smartphones (e.g., GPS, accelerometer, communications data) and wearable biosensors (e.g., electrodermal activity, accelerometer). The second aim is to map the dynamic trajectories of STBs over time. The third aim is to identify short-term predictors of STBs during the 6 months post- hospitaldischarge.Ongoingresearchbytheproposedteamdemonstratesthefeasibilityof:recruiting andretainingtheproposedsamples,intensivelymonitoringthemovertimeusingdigitaldevices,and using analyses of these rich data streams to make discoveries about how STBs and related behaviorsunfoldinnature.Thedatacollectedinthisstudywillprovidearichdatasourcethatwillbe used by our research team and collaborative researchers to advance the understanding, prediction, andultimatepreventionofSTBsandrelatedoutcomes.